Federal authorities have been aware for years that suspected terrorists with ties to Osama bin Laden were receiving flight training at schools in the United States and abroad, according to interviews and court testimony.

Three days after the attack on the Pentagon and the World Trade Center, FBI Director Robert S. Mueller III described reports that several of the hijackers had received flight training in the United States as "news, quite obviously," adding, "If we had understood that to be the case, we would have -- perhaps one could have averted this."

A senior government official yesterday acknowledged law enforcement officials were aware that fewer than a dozen people with links to bin Laden had attended U.S. flight schools. However, the official said there was no information to indicate the flight students had been planning suicide hijacking attacks.

"We were unable to marry any information from investigations or the intelligence community that talked to their use of this expertise in the events that we saw unfold on the 11th," the official said.

Connections between terrorists and flight training include the following:

• In 1996, two flight school operators said last week, FBI agents visited them to obtain information about several Arab pilots connected to a Pakistani terrorist eventually convicted of plotting to bomb U.S. airliners.

The flight schools, Coastal Aviation of New Bern, N.C., and Richmor Aviation of Schenectady, N.Y., were two of four that provided flight training to Abdul Hakim Murad in the early 1990s, according to Philippine authorities. Murad was arrested in Manila in 1995 and later convicted in New York of plotting to blow up a dozen U.S. airliners over the Pacific, then crash a suicide plane into CIA headquarters.

• In 1998, FBI agents questioned officials from Airman Flight School in Norman, Okla., about a graduate later identified in court testimony as a pilot for bin Laden, according to Dale Davis, the school's director of operations.

• This year, the trial of bin Laden associates for the 1998 bombings of U.S. embassies in Kenya and Tanzania yielded documents containing several references to flight schools and bin Laden pilots.

• Two weeks before the Sept. 11 attack, Davis said, FBI agents returned to Norman seeking information about another Airman student, a French-Moroccan dropout who had entered the country on a visa sponsored by the flight school. The man, Zacarias Moussaoui, had been detained in Eagan, Minn., on an immigration violation after he tried to purchase time on a jet simulator -- even though he had never flown solo in a single-engine aircraft.

One government witness in the embassy-bombing trial, Essam al-Ridi, testified that he had taken classes and taught at the now-defunct Ed Boardman Aviation School in Fort Worth. Al-Ridi also said that in the mid-1990s, he purchased a used Saber-40 aircraft on bin Laden's behalf for $210,000 in Tucson. Another witness in the same bombing trial, L'Houssaine Kerchtou, testified that he was sent to a flight school in Nairobi and later served as a pilot for bin Laden.

The issue of how U.S. authorities processed early warning signs that terrorists were taking advantage of the flight school system is certain to be examined in the aftermath of the attack. Suzanne E. Spaulding, executive director of the National Commission on Terrorism, a congressionally appointed task force, said, "In hindsight, we can see how all these things [flight school connections] might be relevant and important." But, she said, "it is harder on a day-to-day basis. There is no question that technology could help sort information."

Since the attack, the FBI has extended its investigation to dozens of flight schools coast to coast, including some of the same schools it visited in the years before the attack. According to law enforcement officials and press reports, the 19 suspected terrorists received flight training from at least 10 U.S. flight schools. At least 44 people sought by the FBI for questioning received some flight instruction.

Dietrich L. Snell, who helped prosecute Murad, said that although the Pakistani terrorist attended four U.S. flight schools, it would have been difficult for the FBI to connect the schools to the kind of terrorist attack that occurred Sept. 11.

Murad, he said, had indicated that he wanted to use his flight training to become a commercial pilot until he was recruited by Ramzi Ahmed Yousef, a bin Laden operative who also plotted the 1993 World Trade Center bombing.

"I think that because Murad had been trained as a pilot it's tempting in hindsight to say that the bureau should have known," said Snell. "But I think they were missing any link that would have connected the flight schools to this kind of terrorism."

The Murad investigation showed that Murad and Yousef were planning to employ five-man teams to smuggle bombs on to 12 planes operated by United Airlines, Delta Air Lines and Northwest Airlines during a two-day period in 1995. Prosecutors for the U.S. government described the plot as "one of the most hideous crimes anyone ever conceived."

Murad confessed to authorities that part of his planned role in the terror attack was to crash a plane into CIA headquarters in Langley.

Richard Kaylor, manager of Richmor Aviation, said the FBI was first alerted to the Schenectady flight school after a Richmor business card was discovered in Murad and Yousef's Manila apartment.

Kaylor said two FBI agents came to interview him about Murad in 1996. He said he provided information about Murad and two other student pilots, both of whom lived with Murad. Kaylor said the three men had come to Schenectady after a stint at Alpha Tango Flying Services in San Antonio.

Kaylor said four FBI agents returned Friday to Richmor to question him about a Turkish student who had received his private pilot's license last year. But Kaylor said it was unclear whether the agents were aware that he had been interviewed five years earlier.

Whether officials at Alpha Tango were also interviewed in 1996 is unclear. The flight school's owner, Hamid Afzal, could not be reached for comment. After the Sept. 11 attack, Afzal contacted the FBI about names on a published list of suspects, believing some of the hijackers might also have taken instruction at Alpha Tango, according to a report in the San Antonio Express-News.

Paul Proctor, the former owner of Coastal Aviation, another school Murad told investigators he had attended, said he could not recall whether the convicted terrorist had received his commercial pilot's license from his facility. But he said he "wouldn't be surprised," because an FBI agent searched his files about the same time agents were visiting Richmor.

Proctor said that the FBI agent never disclosed the purpose of the visit, but that he asked to see the files for students of Arab descent. The agent collected names, passport information and flight training records, according to Proctor. As the agent was finishing, Proctor said, "I made a little comment about hijacking an airplane or terrorism. He said, 'Don't even say that.' That was obviously what he was looking for."

Proctor, whose company ceased operations in 1997, said he had already been suspicious about a specific group of Arab students, two of whom had arrived at the school on North Carolina's coast from New York City in a taxicab. The students already had private pilots' licenses and had come to the school to receive advanced training to fly multi-engine aircraft, Proctor said.

The day after the students completed their training and left, Proctor said, he discovered that a $12,000 instrument radio pack -- including automatic direction finder, navigation aids and transponder -- was missing from one of his single-engine Cherokee Archers. Proctor said he never reported the theft to police because he believed he had little hope of recovering the equipment.

About three years later, FBI agents visited Airman Flight School in Oklahoma to inquire about Ihab Ali Nawawi, a bin Laden associate whose name surfaced during the trial for the 1998 embassy bombings. Dale Davis, the flight school's director of operations, said Nawawi obtained his commercial pilot's license from Airman in the early 1990s, then traveled to another school in Oklahoma City to qualify for a rating to fly small business aircraft.

In testimony during the embassy bombing trial, al-Ridi, the government witness, described Nawawi as a pilot for bin Laden. Al-Ridi testified that he met Nawawi in Khartoum at a time when Nawawi had just graduated from flight school in the United States and had begun to work for bin Laden.